In settings such as small plants, factories, houses or other small-scale systems that utilize single-phase or center tapped-delta power, switching power supplies and variable frequency drives, phase unbalance and harmonic noise present in electrical circuits can cause numerous problems. Phase unbalance with respect to ground is the main source of noise. Voltage balance is probably the single most important aspect of power quality. Just a slight voltage imbalance can damage a motor that is operating at full capacity. Voltage balance is the weak point of rotary and static converters, and even utility three-phase service can be unbalanced enough to harm three-phase equipment. The impact of this problem is evident by the huge industry in manufacturing of devices that monitor phase balance to protect motors. Phase unbalance and resulting harmonic noise can destroy electronic components, increase the number of control lock-ups requiring rebooting, shorten the life of electric motors, and lower system reliability.
These transient voltage spikes and harmonics may be caused by switching occurring at an upstream power-station, switch mode power supplies and variable frequency drives, or numerous other events. Such transient voltage spikes and harmonics can severely damage or destroy equipment connected to the affected single-phase circuit, or, when the system employs circuit interrupters, can cause those interrupters to open the circuit, resulting in power outages throughout the plant. Such outages have negative economic effects since productive equipment remains non-functional until the circuit is re-energized.
Inductors have been used for harmonic mitigation for many years. However, the prior art systems have several shortcomings. Variable frequency drives generate more noise when running with a light load, and inductors, which are current smoothing devices, are ineffective at removing transient electrical noise including harmonics. Such a system causes stress on devices connected to the circuit and may damage or cause permanent failure of the components. Additionally, the solid-state components used in the drive systems are degraded by the harmonics caused by the drive itself. What's more, metal oxide varistors (MOV) based TVSS (transient voltage surge suppressor) will not address the spikes injected at the zero crossing as they are below the clamping voltage but these spikes (noise) can be removed by the Single Phaseback.